1. Field of the Invention
The present invention relates to a sealing device provided to a joint section of a robot. The present invention also relates to an articulated robot in which a joint section is equipped with a sealing device.
2. Description of the Related Art
Typically, in an articulated robot in which a driving mechanism for driving an arm or a wrist is incorporated into a joint section, in order to prevent a lubricant retained in the driving mechanism from leaking out, to the exterior of the joint section, an oil seal, as one type of a contact seal element, is provided in a relatively movable region of an output-end member of the driving mechanism (e.g., a bearing unit at the output side of a reduction gear unit). In particular, in certain applications where it is required to effectively prevent the environment of the robot or an objective workpiece to be operated by the robot from being contaminated due to the operation of the robot, it has been proposed that the joint section be equipped with a sealing device capable of providing overlapped seal portions having a multi-stage configuration, for the driving mechanism incorporated into the joint section.
For example, Japanese Unexamined Patent Publication (Kokai) No. 63-22290 (JP-A-63-22290) discloses a wrist mechanism of a robot adapted to operate in a clean room, which is equipped with a two-stage type sealing device including a grease seal (i.e., a contact seal element) for sealing an output-end member of a reduction gear unit of a driving mechanism incorporated into a wrist housing, and a labyrinth seal (i.e., a non-contact seal element) for sealing a gap between the wrist housing and a movable wrist portion joined to the driving mechanism. In this wrist mechanism, the interior space of the wrist housing is maintained at a negative pressure, so that it is possible to effectively prevent a lubricant retained in the driving mechanism and dust particles generated due to the abrasion of movable members in the driving mechanism from leaking out, to the exterior of the wrist housing or into a clean room.
The sealing device for the wrist mechanism or the joint section of the robot, described in JP-A-63-22290, is configured such that the outer seal portion of the two-stage overlapped seal portions or sealing device is constituted by a labyrinth seal (or non-contact seal element), and thus can effectively seal against dust particles that may be pulled in by the negative pressure into the housing. However, if the lubricant in the driving mechanism passes through the grease seal, forming the inner seal portion of the overlapped seal portions, the above conventional sealing device may not sufficiently seal in the lubricant. Further, since it is assumed that, in JP-A-63-22290, the robot is used in a clean room, in the case where foreign matter, such as dust particles, liquid droplets, etc., exist in the external environment of the robot, it may be difficult to prevent the foreign matter from penetrating through the labyrinth seal into the wrist housing.
For example, in manufacturing lines of products required to be free from contamination, such as food, medicine, etc., an articulated robot provided for handling such products has to reliably prevent not only the lubricant from leaking out of the joint section, but also must prevent washing agents or sterilizing gas blown onto the robot from penetrating into the interior of the joint section. Therefore, in the case of the articulated robot for handling products required to be free from contamination, even if the joint section is equipped with the sealing device described in JP-A-63-22290, it may be difficult to ensure sealing at a required level.